1. Field of the Invention
The present invention relates to an improved plastisol matrix ink releasing member suitable for duplicating and so-called "carbon paper" applications.
2. Description of the Prior Art
In the manifolding and duplicating art, there has been a significant change over the past several years from the total transfer type of "carbon paper" to the ink releasing type. In the total transfer "carbon paper", carbon particles are suspended in a wax medium supported on a paper substrate. Writing or impact pressure applied to an original sheet in contact with the paper substrate caused a portion of the wax layer corresponding to the writing or type face to totally transfer to a copy sheet in contact with the wax surface. Considerable difficulty has been encountered with this paper in view of the softness of the wax layer and its tendency to mark anything it comes in contact with. Also, since the duplicating paper functioned by totally transferring portions of the wax coating, the useful life of the paper tended to be short.
In order to overcome the aforementioned problem, ink releasing duplicating or "carbon papers" were developed. The ink releasing types of "carbon paper" are prepared using a solution or dispersion of a synthetic organic resin, a plasticizer for the resin, a liquid ink vehicle which may also be a plasticizer for the resin and colorant materials. The solution or dispersion is then coated on a suitable substrate and dried by evaporation of a solvent or formation of a plastisol to form a matrix of the synthetic resin containing the liquid ink. The liquid ink is retained within the matrix making the surface of the duplicating sheet clean to the touch. The liquid ink is expressible from the matrix on selective application of pressure. The partially depleted portions of the matrix are restored by the migration of ink from other areas substantially increasing the useful life of the duplicating sheet.
Duplicating sheets prepared from solution are disclosed by Ralph H. Clark in U.S. Pat. No. 2,944,037, issued July 5, 1960, assigned to the assignee of the instant application. Duplicating sheets prepared from plastisol forming dispersions are disclosed by the same Ralph H. Clark in U.S. Pat. No. 2,989,493, issued June 20, 1961, also assigned to the assignee of the instant application.
The ink releasing members of the present invention are an improvement over the plastisol matrix ink transfer composition disclosed in U.S. Pat. No. 2,989,493, which patent is incorporated herein by reference.
The ink-transfer compositions of U.S. Patent No. 2,989,493 were prepared from finely divided polyvinyl chloride resin particles dispersed in liquid organic vehicles containing coloring matter. The liquid organic vehicle was a mixture of a plasticizer operative to solvate the polyvinyl chloride resin particles on heating to the fusing temperature, a heat polymerizable resin to blend with the polyvinyl chloride resin during fusing, and an organic liquid which is substantially non-drying, substantially non-volatile at normal room temperatures, and sufficiently incompatible with and present in sufficient quantity to migrate and to be expressible from the fused resin under pressure. A colorant material such as a dye and/or pigment is carried by the latter organic liquid. The composition can also include minor amounts of catalysts, stabilizers and fillers.
In order to obtain good writing intensity and a reasonably useful life from the ink transfer composition, a large amount of organic liquid vehicle is employed to carry the colorant materials. It was found that 25% to 30% by weight of oils are necessary to produce the proper writing intensity, however, such a large amount presents serious difficulties during the fusion process. To fuse or cure the plastisol, temperatures in the range of 175.degree. C. to 205.degree. C. are necessary. At these temperatures, large volumes of the releasing oils are driven off from the coating surface either polluting the air or requiring extensive equipment to remove the oil from the air. The expense of the wasted oil and the expense for the equipment necessary to control this wasted oil add substantially to the production cost of the ink-transfer member.